1. Field of the Invention
The present invention generally relates to an image forming apparatus, and more particularly, to an image forming apparatus such as a color printer, a color copier, a color facsimile machine, and a multifunctional peripheral.
2. Description of the Related Art
Image forming apparatuses of the electrophotography method can print color images on recording media such as paper and film. Toner of four colors is generally used for color printing. As a result, a color image forming apparatus requires more components than a monochrome image forming apparatus does. Color printing takes more time than monochrome printing does.
Personal computer (PC) users often dispose image forming apparatuses around their PCs, and use the image forming apparatuses as printers. Accordingly, it is desired that an image forming apparatus be short in height and small in footprint.
Users often replace consumable supplies and maintain image forming apparatuses by themselves so as to save time and reduce maintenance cost.
There are two well-known color printing methods, the one drum method and the tandem method.
The one drum method uses one photosensitive unit and multiple developing units disposed around the photosensitive unit. The photosensitive unit is rotated for as many cycles as the number of colors. A monochrome toner image is formed by a developing unit on the photosensitive unit during each cycle of rotation, and superposed into a full color toner image. Finally, the full color toner image is transferred to a recording medium.
The tandem method uses multiple photosensitive units arranged in a line and multiple developing units disposed close to respective photosensitive units. A monochrome toner image is formed by a developing unit on a photosensitive unit, and each monochrome toner image is transferred to a recording medium one by one thereby to form a full color image on the recording medium.
The tandem method is advantageous over the one drum method in increasing printing speed. However, the tandem method consumes more toner than the one drum method does. It is preferred that a developer supply unit, which provides toner (developer) to the developing unit, be provided separately from the developing unit. A separate developer supply unit may be easier to handle than a developer supply unit provided with the developing unit in the same cartridge.
It is preferred that the main body of the image forming apparatus not only be small in footprint, but also have no member protruding therefrom. The top face of the main body may be used as a loading unit on which printed recording media are loaded.
Document No. 1 listed below discloses an image forming apparatus in which a loading unit is formed on the top face of the image forming apparatus, and a developer supply unit is provided separately from a developing unit.
Document No. 2 listed below discloses an image forming apparatus including multiple photosensitive units arranged in a line, multiple developing units arranged in a line, and an intermediate transfer belt; the photosensitive unit, the developing units, and the intermediate transfer belt being disposed at a slant (inclined), instead of horizontally as disclosed in document No. 1, thereby to reduce the footprint thereof.
Document No. 3 listed below discloses an image forming apparatus in which a loading unit is slanted thereby to increase the amount of recording media that can be loaded on the loading unit.
The following documents are known to describe the related art: Japanese Laid-Open Patent Applications No. 2002-362807 (Document No. 1), No. 2002-214868 (Document No. 2), and No. 2003-50351 (Document No. 3).